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Case history of a seventy year old man with myelodysplastic syndrome is presented. The disease terminated into acute leukaemia in 22 months. The pure, B lymphoid stem cell nature of the leukaemic cells has been proved, beside morphology and cytochemistry, by detailed flow cytometric phenotyping and PCR amplification as well as sequencing of the immunoglobulin heavy chain gene CDR3 region.

In this report we summarize our experiences based on the gene rearrangement study of 111 leukaemic patients of different kind. The lymphocyte DNA of the patients was studied for rearrangement of the immunoglobulin light chain constant-, the heavy chain joining- and the T cell receptor beta chain constant region. Our data have well supplemented the results of the monoclonal antibody experiments. In 33 cases the DNA study was in good agreement with the immunological data. In 42 our data helped in gave different results, immunological results. In 11 cases evaluating the DNA and immunological data indicating the necessity of further investigation. The results were inconclusive in 25 cases. As a conclusion we consider the gene rearrangement study to be useful for diagnostic purposes.

Presence of heavy chains (Mu, Gamma, Alfa) of immunoglobulins in plasma cells, in plasma cell precursors and in atypical cells (Sternberg-Reed-, Hodgkin's cells and mirror image cells) was studied by immunoperoxidase technique. In 7 cases all types of the mentioned cells revealed a strongly positive IgG reaction. In 16 cases in atypical cells beside the moderately positive IgG reaction a mild reaction of IgA has also been seen. In these cases only a few plasma cell precursors (plasmoblasts,immunoblasts) have occurred. Considering the first group of patients it can be supposed that atypical cells develop from the plasma cell precursors.